This invention relates to liquid flow control valves for controlling, for example, water flow in a vehicle heating system, of the type having a housing to which hose connections are made, and a valve obturator slidable in the housing relative to a sealing element.
For precise control of the interior heating system of a vehicle valves of the aforementioned type are used in the water circuit of a vehicle heating system for the purpose of regulating the flow of engine-heated water to a heat exchanger which in turn heats air supplied to the interior of the vehicle. For proper heating control it is necessary that the control of the smaller water throughflows be more accurate than the control of the larger water throughflows.
The accuracy of the adjustment of the valve for the control of the smaller water throughflows is to a large extent dependent upon the wear and tear on the valve caused by traces of foundry sand in the cooling water resulting from the casting of the engine block. Although the foundry sand is cleaned out of the coolant passages of the engine after casting of the block, it is inevitable that some sand remains and in use of the vehicle this sand is dislodged, contaminating the cooling water. This sand can become enbedded in the rubber and/or plastics used for sealing elements in the valves hitherto used to control water flow in vehicle heating systems, leading to abrasion of the metal surfaces with which sealing elements cooperate. Eventually this causes the valve to leak, with consequent loss of precision control of small water throughflows.
An object of the present invention is to provide a valve of the aforesaid type which is such that precise control of small water throughflows is maintained over an adequate working lifetime of the valve.